The Great War and its aftermath is the subject of great interest for those who would maintain peace. The causes of the war were many. Here is one conclusion:

Beyond all else, the victories of the armies of Marshal Foch at last refuted the Prussian doctrine practised by Frederick the Great in Silesia, by him and by his successors in Poland, by William I in Schleswig and in Alsace-Lorraine. The archaic conception that the necessities of the strong are sufficient warrant for the plundering and enslavement of the weak fell with the revelation that however long the evil principle may seem to prevail, in the end the concerted efforts of the weak will overthrow the strong.*

What other causes should we avoid in the future in order to deter national aggression?